Thermal relay



July 28, 1936. c. H. CHAPMAN THERMAL RELAY Filed Jan. 19., 1955 up WEEE Q ,i

@@@mwl @M WEM Patented July 28, 1936 PATENT OFFICE THERMAL RELAY Charles H. Chapman, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application January 19, 1935, Serial No. 2,514

7 Claims. (Cl. 200--116) My invention relates to electric switches or relays, more particularly to thermal relays and has for an object the provision of a thermal relay which is simple and inexpensive to construct and reliable in its operation.

In Patent 1,854,007, issued April 12, 1932, to L. J. Weber there is disclosed a thermal relay which comprises a bimetallic element and a movable member normally biased into an abutting engagement with the free end of the bimetallic element. Heating means are provided therefor and when the bimetallic element flexes surliciently so that the free end thereof moves out of abutting relationship with the movable member the movable member is actuated by its biasing means to operate a movable control bar operatively associated with suitable circuit controlling contacts.

While relays of the type disclosed in the Weber patent are simple and inexpensive, some difflculty has been encountered in the operation thereof due partially to the relatively strong biasing force which is necessary to operate the movable member to move the control bar, and the fact that this biasing force on the movable member, which engages the end of the bimetallic element, imposes a relatively great load on the bimetallic element. The amount of work which the element must accomplish in moving to releasing position is accordingly rather large and it is desirable in a relay of this type that the load on the bimetallic element shall be relatively small, so as to provide for low watt input and accurate adjustment of the relay, and that the biasing force on the movable member shall be relatively great in order positively to operate the control bar. Accordingly, it is a further object of my invention to provide a thermal relay of this type in which the load on the thermal element is substantially unaffected by the biasing force on the movable member.

In carrying out my invention in one form I provide a thermalI relay comprising a bimetallic element having a free end, a pivoted latch member lightly biased.' into engagement with the free end of the bimetallic element and a movable Ymember strongly biased to operate a movable control bar when released by the latch. The latch member and the movable member are provided with interengaging latching portions, the paths of movement of which are so related that the force exerted on the bimetallic element by the latch is substantially independent of the biasing force on the movable member, and the two members are disposed adjacent the control bar in overlapping relation so that when the control bar is returned to its normal position by suitable resetting means, the latch member and the movable member will be engaged thereby and respectively returned to their normal latching l l positions.

For a more complete understanding yof my invention, reference should now be had to the drawing in which Fig. 1 is a front view of a three-phase motor starting switch provided with l0 a pair of thermal relays embodying my invention; Fig. 2 is a side view of theswitch; Fig.,3 is a slightly enlarged perspective view of my improved thermal relay with the heater removed and Figs. 4 to 6 inclusive are enlarged frag- 15 mentary sectional views illustrating the operation of the device shown in Fig. 3.

Referring to the drawing, the motor starting switch shown in Figs. 1 and 2 comprises essentially a three pole switchl, rotatively mounted 2@ in the bearings I I on a base I2 and mechanically connected to be operated by an electromagnet I3. Each of the thermal relays I4 embodying my invention is connected to a corresponding one of the circuits controlled by the motor starting 25 switch and is arranged to operate an actuating member or control bar I5 carrying the control contact I6 which is connected in the energizing circuit of the electromagnet I3. The thermal relays are suitably connected in the circuit of the 30 motor starting switch, preferably as shown in the Vabove-referred to Weber patent.

As shown in Fig. 3, each o1' the thermal relays I4 comprises a unitary structure, the termal working parts of which are carried by a channel 35 frame member II of substantially inverted L shape, one end of which is provided with an upturned lug I8 for mounting the frame on a support I9 extending from the base I2. Secured to the frame II is a supporting spring bracket 20 to 40 which a bimetallic element 2| is xedly secured, as by spot Welding. In order to provide for factory adjustment of the bimetallic element 2I, the end of the supporting bracket 20 remote from the r bimetallic element is spot Welded to the frame I'I 4" and an' adjustable screw 22 threadedly engages another portion of the support 20 with the end of the screw bearing against the frame II. It will be apparent that as the screw 22 is adjusted, r the supporting bracket 20 is moved toward or away from the frameV I 'I to adjust the position of the free end of the bimetallic element 2|. When the bimetallic element has been so adjusted to the proper initial position, the supporting 55 bracket 2 8 may be permanently secured to the screw 22 as by placing a drop of solder thereon. The other end of the frame I1 is provided with a pair of supporting ears 23 between which extend a pair of bearing pins 24 and 25. Pivotally mounted on the pin 24 is a movable member 26 a portion of which is disposed adjacent the control bar l5. A spring 21 surrounding the pin 24 engages the frame |1 and the movable member 26 so as to bias the member 26 about its pivot in a clockwise direction as viewed in Fig. 4 to operate the control bar I5. Pivotally mounted on the pin 25 is a latch 28 provided with a slot 29 extending substantially the length thereof, the unslotted end portions of the latch 28 forming latchable and latching portions 30 and 3| respectively. A spring 32 surrounding the pin 25 serves to bias the latchable portion 30 into abutting engagement with the free end 2|' of the bimetallic element 2|, whereby the latch 28 is held in the latching position shown in Figs. 3 and 4. It will be observed that the paths of movement of the latch member and the movable member 26 partially overlap and that a portion of the movable member 26 extends into the slot 29, an extending nger 33 formed thereon being normally engaged by the latching portion 3| of the latch 28 in latching relation as shown in Fig. 4.

It will be remembered that it is desirable in relays of this type that the load on the bimetallic element shall be relatively small and that the biasing force on the movable member shall be relatively great, and accordingly the biasing springs 21 and 32 are respectively arranged to exert a relatively heavy and a relatively light biasing force on the movable member 26 and on the latch 28 respectively, the paths of movement of the engaging portions 3| and 33 being so arranged that the load imposed on the free end 2| of the bimetallic element by the latch 28 is substantially unaffected by the biasing force on the movable member 26. As may be seen by reference to Figs. 4, and 6, the engaging portion 33 carried by the movable member 26 tends to move substantially vertically as-the member 26 `rotates about the pin 24 in a clockwise direction and the latching portion 3| on the'latch 28 tends to move substantially horizontally to the right, as viewed in the drawing, under the bias exerted by the spring 32. Because of this right angle relation of the paths of movement of the engaging portions 3| and 33 it will be seen that the engaging portion 33 exerts substantially no horizontal force on the latching`portion 3| tending to rotate the latch 28 about its pivot and accordingly the load imposed on the bimetallic element 2| by the latch 28 is substantially unaiected by the biasing force of the spring 21. To express the engaging relation of the portions 3| and 33 a little differently, it will be observed that the portion 3| on the latch 28 is arranged substantially radially with respect to the pivot pin 25 so that the line of action of the force exerted on the portion 3| passes through the pivot pin 25 and exerts substantially no rotative moment on the latch 2s. y

Referring again to Figs. 1 and 2, the frame I1 is secured to the support I9 by a. screw 34 which also serves to secure thereto one terminal of a heater 35, the other terminal of which is secured by a screw 36 to a support 31 extending from the base I2, the supports 31 and I8 serving as conducting leads for the heater 35. The heater 35, whichl has the form of a flattened helix, surrounds a substantial portion of the bimetallic element 2| and is preferably of the removable type disclosed in the above-referred to Weber patent. In order that the latch 28 shall be free to move past the heater when the bimetallic element fiexes to release the latch, the free end 2| of the bimetallic element is angularly oiset toward the latch as shown.

As shown, the bimetallic element 2| and the latch 28 are arranged with the latch substantially perpendicular to the main portion of the bimetallic element 2| and it will be apparent that when the element 2| is heated, the free end 2| of the bimetallic element due to its oilset relation to the main portion moves in an arc about the rlxed end of the bimetallic element with respect to which arc the latch 28 is in non-tangential relation. Accordingly, in order for the free end of the bimetallic element to move out of abutting engagement with the latch the bimetallic element must, unless provision is made to prevent it, force the latch 28 backwards against the biasing force on the latch. While the additional load thus imposed upon the bimetallic element is not excessive with my improved lightly biased latching arrangement, I have found that the efiiciency of operation of the thermal relay may be considerably improved by forming the latchable portion 30 of the latch 28 at an angle with the main portion, as shown, so as to provide an engaging surface which is substantially tangential to the arc of movement of the free end of the bimetallic element.

In Figs. 1 and 2, I have shown the motor starting switch in its open position and my improved thermal relays in their normal positions with the control contact 6 in closed circuit position in the energizing circuit of the electromagnet I3. With the starting switch closedby energization of the electromagnet I3 by means oi a suitable switch (not shown) to supply current to a load device, upon the occurrence of abnormal current conditions, one or more of the heaters I5, which are connected in series circuit relation with the associated contacts of the switch Il, will cause the free end of the associated bimetallic element to move outwardly from the position shown in Figf4 to the releasing position shown in Fig. 5 whereupon the latch member 28 will be rotated by the spring 32 to move the latching portion 3| horizontally to the right, thereby releasing the movable member 26 for rotation about its pivot in a clockwise direction to the tripping position shown in Fig. 5 and the control bar l5 will be operated thereby to move the control contact I8 to open circuit position.

In order to reset the control contact I8 to the closed circuit position after the bimetallic element 2| has cooled, a reset button 38 is provided which may be operated to engage an arm 38 extending from the control bar I5 and thereby operate the control contact i8 in a counterclockwise direction about its pivot 48. Due to the yielding mounting ot the contact I8, the control bar |5 may be moved past its normal position to the extreme position shown in Fig. 6, and it will be seen that the control bar l5 engages the latch 28 to move the latch beyond the free end 2 of the bimetallic element and engages the member 28 to operate it to the extreme position there shown. When the reset button 38 is released the movable member 2l and the latch 2l will be returned to their respective normal position shown in Fig.- 4 by the biasing springs 21 and 32, the latchable portion 38 engaging the free end l 2| of the bimetallic element and the portions 3| and'33 engaging each other to prevent further clockwise movement of the member 26.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modications as fall Within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A thermal device comprising a movable member biased from one position to a second position, means including a latch having a latching portion disposed in the path of said movable member for latching said member in said one position, said latch also having a latchable portion, a thermal element having a movable portion disposed in the path of said latchable portion and means for biasing said latch into abutting engagement with said movable portion of said thermal element and for moving said latch to release said movable member when said thermal element moves out of the path of said latch, the respective engaging portions of said latch and said movable member being movable substantially at right angles to each other, whereby the force exerted on said thermal element by said latch is substantially independent of the force exerted on -said latch by said movable member.

2. A thermal device comprising a movable member biased from one`position to a second position, a pivoted latch comprising latching and latchable portions extending outwardly from the pivot point thereof, said latching portion being disposed in the path of said movable member for latching said member in said one position, a movable bimetallic element normallydisposed in the path of said latchable portion of said latch, and means for biasing said latch about said pivot point against said bimetallic element and for rotating said latch to release said movable` member when said bimetallic element moves out of the path of said latchable portion, said movable member being arranged to exert` a substantially radial force on said latching portion of said latch whereby the force exerted on said bimetallic element by said latch is substantially independent of the bias on said movable member.

3. A thermal relay comprising a movable member normally biased from one position to a second position, means including a pivoted latch normally engaging said movable member for holding said movable member in said one position, said latch being biased for rotative movement about its pivot to unlatching position, and a bimetallic element having a movable portion abuttingly engaging said latch for normally holding said latch in latching` position against `the bias thereon, the engaging portions of said latch and said movable member being so arranged relative to the pivot point of said latch that the biasing force on said movable member exerts substantially no rotative moment on said latch, whereby the pressure between said abuttingly engaged portions of said latch and said bimetallic element is substantially unaffected by the bias on said movable member.

4.A unitary thermal device comprising an L shaped frame, a movable member pivoted on one leg of said frame and biased from one position to a second position, a latch pivoted on said one .leg and having a latching portion disposed in the path of said movable'member for latching said member in said one position, said latch including a latchable portion, a bimetallic element having one end xed to the other leg of said frame and having a free end disposed in the path of said latchable portion, and means for biasing said latch against said free end of said bimetallic element and for Amoving said latch about its pivot to release said movable member when said bimetallic element moves out of the path of said latch, the respective engaging portions of said movable member and said latch being arrangedy to move substantially at right angles to each other, whereby the force exerted on said bimetallic element by said latch is substantially independent of the force exerted on said latch by said movable member.

5. In combination with a control device having a control bar movable from one position to a second position and resetting means for returning said control bar to said one position, a thermaldevice comprising an L shaped frame, a movable member pivoted on one leg of said frame and biased to operate said control bar to said second position, means including a latch pivoted on said one leg and having a latching portion engageable with said movable member for latching said member against movement to its biased position, said latching portion being movable substantially at right angles to the path of movement of ysaid movable member whereby the bias on vsaid movable member exerts substantially a radial force on said latch, said latch also having a latchable portion, means for biasing said latch from latching to releasing position, a bimetallic element extending from the other leg of said frame and having a free end normally abuttingly ,engaging said latchable portion in latching position, said bimetallic element being movable out of the path of said latchable portion to release said latch, said latchable portion extending adjacent said movable member in engageable relation with and biased toward said control bar whereby said latch and said movable member are resettable by the return movement of said control bar to said one position.

6. In combination with an electric switch having a control bar movable from one position to a second position and resetting means for returning said control bar to said one position, a thermal device comprising a movable member adjacent said control bar, means for biasing said movable member to operate said control bar to said second position, means inclding a latch pivoted adjacent said movable member having a latching portion engageable with said movable member for latching said movable member against movement by said biasing means, said latching portion extending substantially radially from the pivot of said latch and being movable substantially at right angles to the path of movement of said movable member whereby said bias on said movable member exerts substantially no rotational moment on said latch, said latch also having a. latchable portion, means for biasing said latch from latching to releasing position, and means including a bimetallic element having a movable portion normally abuttingly engaging said latchable portion for retainingsaid latch in latching. position against its bias and movable out of the path thereof to release said latch, said latchable portion extending adjacent said movable member in engageable relation with and biased toward said control bar whereby said latch and said movable member are resetable by the return movement kof said control bar to said one position.

7. A thermal device comprising a bimetallic element having a xed end and a. free end, a heaterv adjacent an intermediate portion of said element, said free end of said element being adapted to move in an arc about said xed end when said element is heated, and a movable member normally biased into abutting engagement with said free end of said bimetallic element, said movable member engaging said element non- .tangentially to said are of movement whereby said member is free to move past said heater when released by said bimetallic element, the portion of said movable member over which said free end of said bimetallic element moves to releasing position being formed at an angle to provide an engaging surface tangential to said arc of movement.

CHARLES H. CHAPMAN. 

